Download 9.2 adaptions and support study guide

9.2.10 Adaptation of Xerophytes and 9.2.4 Plant Support Study Guide
Part 1: Read for Understanding.
Instructions: Read pages 249 & 251, and then address the IB Assessment Statements below:
9.2.4 State that terrestrial plants support themselves by means of thickened cellulose, cell turgor,
lignified xylem
9.2.10 Outline four adaptations of xerophytes that help to reduce transpiration.
Part 2: Guide Notes
Support in Terrestrial Plants & Adaptations
Support in Terrestrial Plants
Some terrestrial plants attain
.
 For example the picture on the left is
of the west coast of
North America.
 These trees reach over 90 m
The support for the enormous trees is provided by three factors:
1.
.
2.
.
3.
.
Thickening of the cellulose cell wall.
 The cell wall’s of supporting tissues of plants are thickened with
.
 Note the
of the cells towards the outer (lower)
sections of this
section.
 The photograph to the right show the thickening of the
of the
.
Lignified xylem vessels

is a highly branched polymer.
 In the diagram to the far left the xylem shows a cylinder
with
annular
.
 Cellulose in cell walls & Lignin in xylem act together to provide support
 Stem cells, including xylem cells occur in
within a plant.
 These act like
to support plant during high winds.
Cell turgidity and plant support:

: Support for plants generated by wall pressures
Water enters the cell by
from the higher osmotic
potential (solute potential) to the lower osmotic potential (solute potential).
o The
forcing the plasma membrane
outwards against the cell wall. A pressure develops called the
, which is excerpted against the cell wall.
o The
is matched by an inward pressure,
equal in magnitude but opposite in direction
o These pressures are called
and
support to the plant tissue. If a
plant experiences a lack of water the cell becomes plasmolysed, wall pressure is lost and the plant
wilts
9.2.10 Adaptations to reduce water loss
 Xerophytic adaptation to reduce transpiration.
o Plants adapted to dry environments are called
.
o Xerophytes are plants that have adaptations to
or indeed to conserve water. They occupy habitats in which there is some kind
of water stress. Examples of such water stress habitats include:
 Desert (high temp, low precipitation)
 High Altitude & High Latitude ( low precipitation or water locked up as snow or ice)
 Rapid drainage (sand dunes)
 Examples of adaptations
o
.
o
.
o
o
o
o
o
o

.
.
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
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
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CAM photosynthesis
o CAM: Crassulacean acid metabolism (CAM) in plants like the Stonecrop reduces water loss by
. This is a Time based alteration of biochemistry.
At night carbon dioxide is combined with phosphoenol pyruvic acid (C3) to form
(C4).
o Oxoloacetic acid is changed to
or aspartic acid. This
until required
for photosynthesis during the day.
o During the day the pore is closed and the malic acid degenerates to PEP (C3) and
.
o Carbon dioxide is then used in
.
 C4 Photosynthesis
o C4: A C4 compound is temporarily stored in the spongy mesophyll (which lack Rubisco for carbon
fixation)
o carbon dioxide is stored in the mesophyll layer by combining with the PEP (C3) to form
as seen before in the CAM plants.
o This breaks down to provide the palisade layer (RUBISCO) with more carbon dioxide.
o Therefore pores can remain open for a reduced time.
Part 4: Practice Questions
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